so the storage area of the garage belongs upstairs, so that you can access the storage area directly through the door at the top in the garage. basically, there would only be the bathroom window there, which can also be done differently.
i also find it strange that the basement stairs and the upper floor stairs are not aligned. that wastes about 2x ~4sqm of space, which at the usual 1600€/sqm is quickly about ~6000€ extra costs (+ possible additional costs because there are 2 staircases including everything that belongs with them).
you want this hallway area with stairs going up in half the living room (basically a lot of wasted hallway space without use or wall space for cabinets), you also want to build with an architect. purely in terms of functionality, that is not a very smart choice. you have a hallway area without a front door of 3x5 meters, where only a staircase stands. that's 15sqm wasted (because the actual entrance still has to be added).
the best thing would be to mentally go through various scenarios (as mentioned above with a stroller after shopping and carrying groceries into the kitchen) and consider whether you like it and where it could be too tight or similar.
in the attic, the hallway is also really wide, bedroom 2 looks pretty skinny. the niche there should at least be about 2.1 meters finished size, so that you can get a bed in there (measure the bed lengths again beforehand :) ). that way the room could still be saved and also be well divided (in adolescence with a separate sleeping area).
the sauna is designed too small. a sauna where you can only sit is nonsense and quickly becomes a broom closet. if you're going to do it, do it properly. you need about 2.3 meters length (outer dimension) so you can lie down inside. width starts at about 1.6 meters. do you want a wet room sauna with tiles and so on? then it would work as drawn. a sauna with wooden walls (dry sauna for ~100°C) needs air circulation to the house wall and would therefore be a step smaller. if you want a sauna, you should at least visit a sauna manufacturer once beforehand and see what you like and just get an offer. we planned a sauna in the upper floor bathroom and also executed it.
don't forget the power connection for 3 phases (400 volts) :)